Exemplary embodiments of the invention generally relate to a rotary wing aircraft, and more particularly, to a brake assembly configured to stop the rotation of a rotor shaft of a rotary wing aircraft.
A conventional disc brake assembly for the rotor of a rotary wing aircraft includes a steel disc which is coupled to a rotating component of the drive system, such as a flange of a shaft for example, using a plurality of bolts such that the disc rotates in unison with the rotor shaft. A brake caliper is mounted to the transmission housing and is positioned adjacent each side of the disc rotor. The brake caliper holds disc brake friction material pads in a position relative to the disc such that the pads can be applied to each side of the disc rotor. The brake caliper is hydraulically actuated from an assembly which displaces brake fluid through a brake line to the caliper. The brake fluid is introduced into the caliper under high pressure causing one or more movable pistons to force the pads into contact with the disc thereby stopping the drive system and thus the main rotor.
During activation of the rotor brake system, the torque created by the rotor system passes through the rotating component, the bolts, the disc, and the caliper assembly. The thru holes used to couple the disc to the rotating component create very high stress concentrations in the disc, therefore limiting the design to materials with high yield stress allowables, such as steel. Steel, however, is not a preferred material due to weight, susceptibility to distortion from thermal cycles, and corrosive properties. When the caliper is engaged, the high friction pads contact the disc surface creating thermal cycles which distort the disc. If the disc becomes distorted, the contact surface area between the pads and disc decreases, making the system less efficient. Furthermore, a layer of surface corrosion may result on a steel disc due to normal exposure to the environment. When the brake engages, the top layer of corroded material is removed, providing no benefit in stopping the drive system, and ultimately causing the disc to wear quicker. As a result of these factors, the steel disc has a smaller reliability factor, reduces fatigue life of the brake assembly, and is more susceptible to damage and failure.